The present invention relates generally to a system for enriching magnetic ore concentration in a feed material. More particularly, the present invention relates to a ultrasonic magnetic separator for enriching magnetite concentration in iron ore.
As steelmaking processes become technologically more advanced, the raw materials used in the steelmaking processes are required to conform with more stringent standards. For example, "commodity grade" iron ore for use in blast furnaces must have a gangue concentration of less than 5 percent by weight. Iron ore used in the production of direct reduced iron pellets must have a gangue concentration of less than 2 percent by weight.
To attain either of the preceding gangue concentrations, it is typically necessary to beneficiate iron ore to reduce the gangue concentration in the iron ore. The required degree of processing and the expense associated with the benefication process depends on the initial gangue level as well as the hardness of the iron ore. For example, the major domestic iron ore, taconite ore, requires a significant degree of processing because the gangue is intimately associated with the magnetite.
An initial step in the iron ore benefication process involves grinding the iron ore. Components in ground iron ore may be classified into three categories: free magnetite, middlings, and free silica. Middlings and free silica are collectively referred to as gangue.
Middlings contain magnetite and silica that are intimately mixed together. Because middlings contain a mixture of magnetite and silica, more finely grinding middlings releases more free magnetite and free silica, which allows a higher percentage of silica to be separated from magnetite.
Conventional iron ore benefication processes typically involve grinding the iron ore to between 80 and 90 percent by weight less than 45 microns, which liberates magnetite from gangue. Gangue may then be separated from magnetite using magnetic separation techniques.
While more finely grinding iron ore theoretically allows the iron ore to be enriched to a greater degree because a higher percentage of middlings are broken down into magnetite and gangue, the efficiency of conventional benefication processes decreases as the iron ore particle size decreases because competing hydrodynamic and inter-particle forces within the magnetic separator cause silica to be entrained with the magnetite and carried into the iron ore concentrate. For example, standard intensity drum-type magnetic separators perform optimally when the iron ore is ground to a particle size of between 10 and 1,000 microns.
Enriched iron ore obtained from prior art benefication processes relying solely on grinding and magnetic separating have gangue concentrations of between about 5 and 6 percent by weight, which makes the iron ore unacceptable for use in many steelmaking processes. To further reduce the gangue concentration, silica floatation processes are typically utilized.
Silica floatation processes require chemical reagents to be mixed with the iron ore. While silica floatation processes enable the gangue concentration to be reduced to approximately 4 percent by weight, the use of chemical reagents significantly increases the cost of the benefication process. The chemical reagents also necessitate that effluent generated from the floatation process be purified before the effluent is disposed of or reused.
Floatation techniques also experience a decrease in efficiency when processing ultrafine particles. For particles smaller than 10 microns, floatation recovery falls steadily. Below 1 micron, separation efficiency using floatation techniques becomes unacceptable.
Subjecting an iron ore slurry to a preliminary ultrasound treatment and then separating the iron ore slurry with a magnetic separator is described by Rychov et al. in Effect of Ultrasonic Treatment of Magnetite Slurry on the Indicators of Magnetic Enrichment. Rychov et al. indicates that this preliminary treatment allows the iron ore level in the iron ore concentrate to be increased by 1.13 percent. The maximum iron concentration produced during Rychov et al.'s studies was 64.84 percent.
In an article entitled Magnetic Separation in Alternating Fields, Goodluck et al. discusses using an alternating current high gradient magnetic separator. Goodluck et el. indicates that the alternating current magnet was operated at 550 volts and 60 hertz so that a field of 600 gauss was generated by the magnet.
Goodluck et al. describes enriching an iron ore slurry by passing the iron ore slurry through a cylindrical canister having an inner diameter of 3.8 centimeters. The cylindrical canister was packed with a stack of wire mesh pieces that were arranged to form a matrix. In one configuration, Goodluck et al. describes that the matrix had a length of 3 centimeters and that the wire mesh had a diamond shaped hole of 4 millimeters by 2 millimeters. Goodluck et al. further indicates that mechanically vibrating the separator increases the enrichment of the iron ore.